I used mobil 1 4T 10w40 prior to switching to amsoil 20w50. Heard and read about how it reduces engine noise and shifting becomes smoother, so i decided to give it a shot. After a 40 mile ride, my bike shifts like crap and 1st to 2nd gear @#$#$%#$%@#%. With mobil, 1st to 2nd shifts had a clunk to it but never ever failed to go to 2nd. With amsoil, I feel like not going to have a 2nd gear after 1000 miles if I continue use crap. It grinded a few times and failed to go to 2nd 3 times. Oh, did i mention that this has never happened with mobil 1. The engine noise is about the same and the engine seems to feel a little hotter (outside temp 74 deg) but, I have no way confirming that. I going to give amsoil another 100 miles. If the shifting doesn't get any better, I'm dumping that sucker out and going back to mobil 1.